1. Field of the Invention
The present invention relates to media feed mechanisms. More particularly, the present invention relates to a variable stiffness friction buckler for the media feed mechanism to prevent multi-sheet feeding of recording media wherein two or more sheets are fed during a single sheet feeding operation.
2. Description of the Related Art
In a conventional single sheet printer, sheets from a media stack are indexed from the stack into the printer feedpath so as to begin a printing cycle. This operation is commonly known as sheet picking and is performed by advancing the uppermost sheet from the media stack using a motor driven roller in an arrangement sometimes referred to as a media feed mechanism which may include a rotational indexing or auto-compensating mechanism. The roller of the auto-compensating mechanism rotates against the surface of the uppermost media sheet to direct that sheet into the media feedpath for printing or other processing involving auto-document feeding.
Multiple sheet misfeeds are a common problem associated with sheet media feeding systems. As the uppermost sheet is picked from the stack of sheet media in the input tray, the next-to-top sheet or sheets are sometimes drawn into the feed mechanism by frictional forces between the top fed sheet and those beneath it. If these lower sheets are not cleared from the feed zone, then multiple sheets are likely to be drawn into the feed zone during the next print cycle resulting in a misfeed. This problem is prevalent where the media stack is stiff and is characterized by higher frictional forces between the media sheets. The problem is also prevalent when the stack is low, rendering the media stack stiffer than a thicker media stack. Accordingly, various separating means have previously been suggested for separating a top sheet of a stack of sheets of media from the next adjacent sheet.
Another consideration is the media weight. Additionally, a roller surface having a coefficient of friction high enough to separate a relatively heavy media such as cardstock, envelopes, and labels, for example, without causing the feed motor to overload will result in more multiple sheet feeding of a relatively light weight media with high friction between sheets such as bond or xerographic paper, for example. A printer needs to be capable of printing both heavy and light media to have a sufficient market.
In order to avoid such multiple sheet misfeeds, some printers have been fitted with a separator which uses friction to buckle the uppermost media sheet and inhibit multi-sheet feeding. However, the problem has still existed that as a media feed stack decreases in height during feeding, the stiffness of the media stack increases rendering feeding more difficult, and multi-sheet feeds and motor stalls more likely.
What is needed is a mechanism, which separates media in a media stack during feeding, inhibits multi-sheet feeds, and which compensates for change of stiffness in a media stack during the media feed process.